Mechanical, microstructural, and radiation shielding characteristics of sustainable high-strength concrete incorporating recycled wastes blended powders

Abstract This study investigated the influence of blended powders of dealuminated metakaolin (DK), limestone (LS), and silica fume (SF) as partial cement replacements on the properties of high-strength concrete (HSC). Nine concrete mixes were designed, including a control mix and mixes incorporating binary, ternary, and quaternary blends of SF, LS, and DK at varying cement replacement levels. The experimental program evaluated the physical properties (slump, setting times, consistency), mechanical properties (compressive and tensile strengths), and microstructure (SEM, XRD, and EDX analysis) of the investigated concrete mixes. Furthermore, radiation shielding properties of the produced concretes were assessed using Monte Carlo (MC) simulations and Phy-X software. The analysis covered both γ-rays and fast neutrons. Results showed that quaternary blends of DK, LS, and SF reduced slump due to higher water demand, while their increased content enhanced compressive and tensile strengths. Optimal strength values were achieved with specific blend ratios: mix 4 (10% DK) for binary blends, mix 6 (15% SF+10% DK) for ternary blends, and mix 9 (15% SF+10% LS+10% DK) for quaternary blends. These optimal mixes exhibited compressive strength increases of 37.3%, 43.35%, and 23.4%, and tensile strength increases of 15.3%, 32.4%, and 22.25%, respectively, compared to the control mix. SEM analysis showed fewer voids and microcracks and a denser microstructure in the optimal replacement mixes. Furthermore, XRD and EDX analyses confirmed that DK, LS, and SF promoted the formation of calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) through pozzolanic reactions. The γ-ray attenuation tests indicated modest improvement in γ-ray shielding capacity of HSC, with DK10 and SF15LS10DK10 mixes recording the highest linear attenuation coefficients (LAC). This improved performance is attributed to their elevated densities (2.47, 2.45 g cm −3 ) and substantial iron content (1.53% and 1.92%, respectively). Additionally, DK10, SF15LS10, and SF15LS10DK10 mixes exhibited excellent neutron shielding, achieving a removal cross-section (FCS) value of 0.086 cm⁻ 1 , with the lowest half value layer (HVL FCS ) of 8.059 cm, and relaxation length (λ FCS ) of 11.627 cm.